1. Field of the Invention
The present invention relates to the field of liquid crystal displaying, and in particular to a liquid crystal display device.
2. The Related Arts
Liquid crystal display (LCD) has a variety of advantages, such as compact device size, low power consumption, and being free of radiation, and is thus widely used. Most of the LCDs that are currently available in the market are backlighting LCDs, which comprise a liquid crystal panel and a backlight module. The working principle of the liquid crystal panel is that liquid crystal molecules are interposed between two parallel glass substrates and a plurality of vertical and horizontal fine electrical wires is arranged between the two glass substrates, whereby the liquid crystal molecules are controlled to change direction by application of electricity in order to refract light emitting from the backlight module for generating images. Since the liquid crystal panel itself does not emit light, light must be provided by the backlight module in order to normally display images. Thus, the backlight module is one of the key components of an LCD. The backlight module can be classified as two types, namely side-edge backlight module and direct backlight module, according to the position where light gets incident. The direct backlight module arranges a light source, such as a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED) at the back side of the liquid crystal panel to form a planar light source that directly provides lighting to the liquid crystal panel. The side-edge backlight module arranges a backlight source, such as an LED light bar based light source, at an edge of a back panel that is located rearward of one side of the liquid crystal panel. The LED light bar emits light that enters a light guide plate through a light incident face of the light guide plate and is projected out through a light exit face after being reflected and diffused to thereby form, after transmitting through a set of optic films, a planar light source to be provided to the liquid crystal panel.
Both the direct backlight module and the side-edge backlight module comprise a set of optic films. A liquid crystal panel is set on the backlight module to directly confront the optic films. The optic films that are currently used include a lower diffusion plate, a prism plate that is disposed on the lower diffusion plate, and an upper diffusion plate that is disposed on the prism plate. The lower diffusion plate functions to concentrate light emitting from the light guide plate for uniform projection onto the prism plate, while the upper diffusion plate functions for hazing the light projecting from the prism plate to effect homogeneous emission of light and elimination of side lobe light shape thereby eliminating irregularity of brightness and darkness (being bright at front view angle and side lobe but dark therebetween) for observation made at a given view angle. However, the existence of the upper diffusion plate causes deterioration of gain of luminance to some extents. Experiments show that removing the upper diffusion plate will increase the luminance gain by 10%. An optic film assembly with the upper diffusion plate removed is generally used in small-sized displays that require low optical grades, such as display of notebook computer or display of desktop computer.
For large-sized liquid crystal displays, with the consideration that observation may be made at various view angles, to avoid non-homogeneous brightness, the side lobe must be properly removed. This requires the use of the upper diffusion plate so that homogeneity of brightness can be obtained at the expense of deterioration of luminance gain so that the optical grade of the large-sized liquid crystal display can be improved. This has been the common technical consensus of the industry.